The skin is the largest organ of the human body. It plays a key role in protecting the body against pathogenic invasion, physical trauma, and excessive water loss. These functions are achieved largely by the outermost layer of the skin called the epidermis. The epidermis is composed of four to five sublayers, of which the stratum corneum is the outer most layer. The stratum corneum contains dead skin cells mixed with natural oils known as lipids, and hydrophilic components that attract water. Lipids are produced by live skin cells in the dermis, a layer underlying the epidermis. Lipids minimize water loss from the stratum corneum and keep chemicals and pathogens from entering the body. Thus, both the lipids and the hydrophilic components are necessary to retain water in the skin.
Properly hydrated stratum corneum makes the appearance of the skin soft, supple, and dewy. However, the stratum corneum can be easily damaged due to various factors, such as friction, weather, chemical irritants, organic solvents, surfactants, and hormonal imbalance. The damage is frequently associated with abnormally high transepidermal water loss (TEWL) (i.e., loss of water from the stratum corneum via diffusion and/or evaporation). Under normal conditions, some TEWL is necessary in order to control the skin's water content and maintain it in dynamic equilibrium with the environment. However, an excessive TEWL causes the skin to become dry, dull, red, and/or flaky. These symptoms are also accompanied by tight, itchy, and/or painful sensations. In more advanced cases, fish net-like cracks or bleeding can occur. If untreated, dry skin can lead to dermatitis, swelling, and infection. Even if the condition is mild, chronically dry skin often results in premature aging of the skin.
Thus, there is a need to effectively hydrate the stratum corneum in order to prevent or repair the aforementioned damage. There are mainly two mechanisms by which the skin can be hydrated: 1) applying a hydrophobic barrier (“film former”) to the skin that mimics the function of the endogenous lipids, or 2) applying hydrophilic agents such as humectants to the skin for attracting water.
Traditionally, film formers have been used to minimize TEWL. Hydrophobic lipids such as petrolatum, lanolin, fatty acids, triglycerides, and phospholipids are a few examples of film formers. Popular commercially available products that contain film formers include Aquaphor™ Ointment by Beiersdorf Inc. and Vaseline™ Petroleum Jelly by Unilever. The film formers in these products form an inert, occlusive film or membrane which retards TEWL by preventing water evaporation from the stratum corneum. However, film formers do not replenish moisture in the stratum corneum, but merely provide a surface coating on the skin. In addition, film formers impart a greasy feel to the skin that deters many consumers.
Humectants are used as moisturizers to attract water by mimicking the role of hydrophilic components of the stratum corneum. Examples of popular humectants include glycerin, propylene glycol, and urea. When applied to the skin, humectants are absorbed into the stratum corneum and draw water from both the dermis and the atmosphere. Due to their ability to hold moisture, humectants enable the skin to maintain higher than normal equilibrium moisture content. One drawback of humectants is “tack” or “drag” feel on the skin during or after application. Another, yet more serious, problem is their inability to prevent evaporative water loss from the skin. This drawback becomes prevalent in a dry environment, where moisture escapes into the atmosphere, while the humectants continue drawing water from the deeper layers of the skin. This inadvertently results in increased skin dryness.
In order to prevent undesired water loss, film formers are often combined with humectants. However, this combination often causes surface build-up on the skin, which could become comedogenic (i.e., tending to produce or aggravate acne). Moreover, the combination of humectants and film formers may not always achieve the desired hydration level in the skin, requiring repeated application. This is impractical and uneconomical from the consumers' perspective.
Thus, formulators are now looking for more effective and practical methods to improve hydration. Recently, minerals have been garnering much attention as their health benefits are discovered. Minerals, in a broadest sense, refer to a naturally occurring inorganic elements or compounds with a characteristic chemical composition and structure. They are essential to the nutrition of humans, animals, and plants. Minerals range in composition from pure elements and simple salts to very complex structures with thousands of known forms. Minerals also play an essential role in enzymatic reactions in biological systems. Minerals that are important for cellular function include calcium, iron, copper, zinc, magnesium and silicon. They are often found in commercial supplements as trace nutrients.
An example of prevalent health benefits offered by topical application of minerals is the Dead Sea. The Dead Sea comprises a unique mineral composition, including minerals comprising magnesium, potassium, calcium, and sodium. The combination of minerals in the Dead Sea is known to alleviate many skin ailments such as psoriasis, eczema, and dermatitis. Some experts even claim that washing the skin with mineral water can help reduce common skin irritations and increase the skin cells' ability to absorb moisture. Recently, it has been discovered that certain types of copper peptide complexes possess both tissue protection and repair properties. One example is a human copper peptide complex, glycyl-1-histidyl-1-lysine:copper(II) complex (“GHK-Cu”), developed by Loren Pickart, PhD. Clinical studies have reported improvements in skin elasticity, thickness, and firmness with the use of GHK-Cu. Currently, GHK-Cu is utilized in several anti-aging products available from Neutrogena Corporation, such as Neutrogena Visibly Firm® Night Cream and Neutrogena Visibly Firm® Eye Cream.
Apart from minerals, yeast extracts have been gaining popularity for their ability to improve skin hydration and complexion. In particular, the specific species of yeast Saccharomyces cerevisiae, known as the “brewer's yeast,” is commonly used for skin care preparations. If processed under proper conditions, the bio-molecules of yeast cells maintain their active forms. These active forms of yeast bio-molecules have been shown to regulate the skin's biochemical pathways in vitro. For example, a composition containing Saccharomyces extract is thought to hydrate the skin by stimulating biochemical activities of certain skin cells keratinocyte and fibroblast. (See U.S. Pat. No. 5,840,309). Many consumers report immediate improvement in their skin complexion after using products containing yeast extracts.
Over the past years, the two cosmetic fields of minerals and yeast have merged to produce bio-chelated minerals. Bio-chelated minerals are obtained by growing yeasts in a medium enriched with minerals in the form of inorganic salts. Through a series of growth and division, the yeast culture absorbs and processes the added minerals. The resulting yeast extracts contain the minerals chelated by the yeasts' biomolecules, more commonly known as bio-chelated minerals. Bio-chelated minerals are very diverse, as various combinations of yeast species and minerals are possible. Bio-chelated minerals may contain the same trace elements as their counterpart minerals such as inorganic salts and peptide complexes, but their properties are very different. For example, Vinson, et al. orally administered various forms of minerals to rats to demonstrate that a bio-chelated mineral is the most bioavailable form of trace elements. (J. A. Vinson, et al., Comparison of the Bioavailability of Trace Elements in Inorganic Salts, Amino Acid Chelates and Yeast, Proceedings on Mineral Elements, 615-621 (1981)). Moreover, our research has unexpectedly revealed that when a certain combination of bio-chelated minerals and a humectant mixture is applied to the skin, an exceptional hydration of the stratum corneum is achieved. Specifically, a bio-chelated mineral blend containing six minerals (silicon, magnesium, copper, iron, zinc, and calcium) proved to be a superior combination for skin hydration.